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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

232                                 ORDINARY BRONZES

wire with about one-third of its weight of pure sulphur and heated in a
current of hydrogen to constant weight: ZnS X 0-6709 — Zn.

(d) DETERMINATION OF THE ALUMINIUM. The liquid from which the
zinc has been removed is concentrated in a porcelain dish to small volume,
the iron being then oxidised with hydrogen peroxide and the solution ren-
dered alkaline with pure potassium hydroxide solution, boiled, diluted
with boiling water and filtered. The filter is washed with hot water and
the filtrate acidified with nitric acid, rendered alkaline with ammonia and
heated to boiling for a short time. The precipitated aluminium hydroxide
is filtered off, washed, dried to some extent, ignited in a platinum crucible
and weighed : A1203 X 0-5303 = Al.

3. Determination of the Phosphorus, Sulphur, Arsenic, Bismuth,
etc.—See Ordinary Brasses.

*
* *

Of these complex brasses the one most largely used is the so-called " Delta
metal," of the following mean composition : 54-62% Cu, 38-40% Zn, 0-5-3%
Mn, 0-4-1-2% Fe, 0-02-2-5% Al, 0-0-5% Pb and0-3% Sn.

ORDINARY  BRONZES

Analysis of ordinary bronzes includes, besides determinations of the
constituent metals (copper, tin and sometimes zinc), also those of the
extraneous metals often present in small quantities (lead, iron, antimony,
nickel, manganese, phosphorus, arsenic, sulphur, etc.). Electrolytic or
gravimetric methods may be used.

A. Electrolytic  Method

In a covered beaker, 1-3 grams of the alloy, as filings or turnings, are
treated in the cold with 15-20 c.c. of nitric acid (D = 1-3), the liquid being
heated gently when the action slackens and finally evaporated almost to
dryness.

1. Determination of the Tin.—The residue is taken up with a few
drops of nitric acid, 50 c.c. of water being mixed in and after about an hour
on the water-bath, the liquid filtered through a compact filter-paper and
the residue on the filter washed with hot water acidified with nitric acid
(i of acid to 100 of water). The filtrate is utilised as described in 3 (below).
The metastannic acid separated may be dried, ignited and weighed, but it
may contain various impurities (especially copper and phosphorus), and
when an exact analysis is required the following procedure is advisable.1

1 The method of fusion with sulphur and sodium carbonate indicated for the gravi-
metric analysis of bronzes (see p. 234) may also be used and, when the antimony has
been removed by means of hydrogen sulphide, the electrolytic method followed.

Further, in absence of phosphorus and antimony the following simpler procedure
may be employed. The impure stannic oxide is separated and weighed and then dis-
integrated with sulphur and sodium carbonate, the resulting fused mass being taken
up in hot water. The copper sulphide is separated and determined and the correspond-
ing weight of the oxide deducted from the sum, SnO2 + CuO. The remainder repre-
sents pure stannic oxide, which gives the tin present in the sample. The copper occluded
in the stannic oxide is added to the amount found in the nitric acid solution.boiling solution of 6-7 grams of ammonium oxalate in a little